The present invention concerns improvements in negative dobbies for forming the warp shed in weaving looms. The object of these improvements is to reduce the stresses, to damp vibrations and deaden noises and to improve the working precision of these machines, so as to allow a more efficient and rational use thereof in combination with looms working at high and very high speeds, as those already in use and now increasingly expanding.
In technique there are known to be negative dobbies for looms, wherein the engagement between the hooks pivoted on the rockers and the respective crooks, takes place after such crooks--already positioned for engagement--have been caused to oscillate by the hooks. In the known arrangements of this type, the engagement between the crooks and the hooks can be obtained only after said hooks have performed a short idle stroke, shifting beyond said crooks so as to take up a position of positive engagement. It is easy to understand the importance of limiting as far as possible the extent of said idle stroke, in order to reduce impact when engagement takes place, especially if the dobby--having to adapt itself to the speeds of faster looms--has to work at high speeds, thereby increasing the accelerations of its moving component parts. It is equally important to prevent the hooks from hitting too forcefully against the crooks, when touching them to cause their oscillation allowing subsequent mutual engagement.
Reducing all these impacts, which follow at very frequent intervals and close distances, means in fact reducing the vibrations in the machine and consequently the noises and the wear of its parts; an increased working precision is thereby obtained, with an improved weaving performance. Finally, the control of the machine on the heald frames results greatly improved, determining an increased stability thereof, with advantageous results as far as quality of the production.